Many different types of filter assemblies have been developed heretofore for various filtering applications. One of the most popular and commonly used filter assemblies is in the form of a flat panel. Such filter assemblies generally consist of a filter element supported by a surrounding peripheral frame, and are usually of relatively inexpensive construction for removal and replacement as a unit.
Pleated filter elements are typically used to increase the filtering surface area and thus efficiency of such filter assemblies, however, there are some difficulties associated with the use of pleated filter elements. For example, pleated filter elements usually include both zigzag and straight edges requiring different sealing techniques with the frame. This can be a significant cost factor in such disposable assemblies.
Attempts have been made to alleviate this sealing problem by folding the ends of the pleats to facilitate engagement along opposite sides of the filter element. For instance, U.S. Pat. No. 4,151,095 assigned to Donaldson Company, Inc., shows a pleated filter element wherein opposite ends of the pleats are folded over diagonal score lines extending at forty-five degree angles from the intersections of the transverse fold lines of their adjacent pleats and the edges to points on the fold lines of their respective pleats. The inwardly folded edges of the pleats and the outwardly folded sides of the endmost pleats are then clamped between suitable retaining structure on the frame for sealing purposes. U.S. Pat. No. 3,640,396 shows a pleated filter element wherein opposite ends of the pleats are folded over diagonal score lines extending at sixty degree angles from points on the transverse fold lines to points on the edges inwardly from the adjacent fold lines defining the pleats.
Other difficulties associated with the use of filter assemblies having pleated filter elements have centered around the fact that they are pre-assembled with the pleated filter elements usually being glued or potted in place in their frames. The attitude of the filter during storage and shipment can be critical. It is best if they are shipped in horizontal position, or at least in a vertical position with the pleats vertical to minimize the effect of shocks on the filter assembly, which in turn can cause disconnection of the zig-zag ends of the pleats and thus bunching. If, for example, about 25% of the pleats become bunched together, this in turn can cause a reduction of about 50% in the filter capacity upon installation. Another related problem is that many filter assemblies simply are not being changed at the recommended intervals because they are relatively bulky and thus difficult to handle and store.
Heretofore there has not been available a pleated filter element which is particularly adapted for shipment in collapsed condition and which when expanded provides controlled expansibility and pleat spacing characteristics to facilitate use as a replaceable filter element. Nor has there been available a frame which is particularly adapted to receive such a replaceable pleated filter element. There is thus a need for such a filter.